Earlier reports estimated around 200,000 litres of sulphuric acid was on board when the accident occurred, but revised reports on Tuesday placed the load at 819,000 litres.

"Assessments to date indicate that one of the carriages has likely ruptured and it is possible that up to 31,500 litres of acid has leaked out," QLD Police said in a statement."

"No other ruptured carriages have been identified as leaking at this stage."

An emergency declaration and two kilometre exclusion zone is still in place as emergency services manage the scene. Despite the leakage, police said initial testing by the Department of Environment and Heritage Protection "indicates that the nearby Horse Creek waterway has not been adversely affected by any leakage."

Emergency services are still investigating the cause of the derailment, with crews planning to work on the site through the day depending on weater conditions.

"The Flinders Highway remains closed in both directions between Julia Creek and Richmond as a result of flooding and the exclusion zone. It is anticipated that the exclusion zone will be in place for least another 48hrs," police said.

"The Queensland Police Service continues to work with other emergency services, Queensland Rail, government and industry partners to manage the situation."